[cfe-dev] Objective-C++11: concerns about adding static_assert support to @interface / @implementation?

[Nico Weber via cfe-dev]

Patch: https://reviews.llvm.org/D59223

On Sat, Mar 9, 2019 at 1:24 PM Aaron Ballman <aaron at aaronballman.com> wrote:

> On Fri, Mar 8, 2019 at 8:10 PM Erik Pilkington
> <erik.pilkington at gmail.com> wrote:
> >
> >
> >
> > > On Mar 8, 2019, at 4:51 PM, Aaron Ballman <aaron at aaronballman.com>
> wrote:
> > >
> > > On Fri, Mar 8, 2019 at 11:52 AM Nico Weber <thakis at chromium.org>
> wrote:
> > >>
> > >> On Fri, Mar 8, 2019 at 11:23 AM Aaron Ballman <aaron at aaronballman.com>
> wrote:
> > >>>
> > >>> On Fri, Mar 8, 2019 at 11:20 AM Nico Weber via cfe-dev
> > >>> <cfe-dev at lists.llvm.org> wrote:
> > >>>>
> > >>>> Hi,
> > >>>>
> > >>>> I'm trying to enable -Wextra-semi in Chromium. I'm almost there;
> the last remaining issue is that we have a macro THREAD_CHECKER(name) that
> expands to nothing in release builds but to `ThreadChecker name` in debug
> builds. It's supposed to be used like
> > >>>>
> > >>>> class C {
> > >>>>  THREAD_CHECKER(checker_);
> > >>>> };
> > >>>>
> > >>>> And then in the implementation, you do
> CHECK_CALLED_ON_VALID_THREAD(checker_); which again does nothing in release
> builds but calls a method on checker_ in debug builds.
> > >>>>
> > >>>> Since this is a declaration, this triggers -Wextra-semi. I figured
> the way to spell the usual `do {} while (0)` you tag on the end of a
> statement macro to silence this warning could be `static_assert(1, "")`, so
> I changed THREAD_CHECKER() to expand to that in release builds instead of
> nothing.
> > >>>>
> > >>>> This works beautifully, but Objective-C interfaces don't support
> static_assert()s as I have learned. So I'd like to add support for that.
> > >>>
> > >>> Do they support _Static_assert() instead (the C11 spelling)
> > >>
> > >>
> > >> No.
> > >
> > > Good to know!
> > >
> > > I'd also like to see _Static_assert() supported in Objective-C and
> > > static_assert() supported in Objective-C++; I think they'd be useful.
> > > However, I'm not certain of the relationship between ObjC/C++ versions
> > > and the language standard version of C/C++ and whether there might be
> > > concerns there.
> >
> >
> > My understanding is that we try to be as compatible as possible with the
> base language, so -xobjective-c++ -std=c++11 should behave just like
> -std=c++11, but also have objective-c stuff. Thats what we do in general
> with static_assert/_Static_assert here too, its just that for some reason
> we don’t parse them in this context.
>
> Ah, nice to know, thank you Erik. Then yeah, count me as a +1 for
> supporting this.
>
> ~Aaron
>
> >
> > Erik
> >
> >
> > >
> > > ~Aaron
> >
>
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